In this project, Scanning electron microscopy is applied to observe the shape and size of three kinds of pollens. Pollens from different plants have different size and shape. Light microscopy is also used to observe the pollens. With light microscopy, different ages of pollens are found. Also the coloration of pollens is found through the light microscopy. X-ray analysis is used to detect the rough compositions. Carbon and oxygen are found for all these pollens. Scarce amount of Phosphorus only exist in the Jonquilla Daffodils. Assuming that the composition of pollens is C16H32O, the electron flight simulator is used to simulate the interaction between electron beam and samples.

Introduction

Pollen, or flower sperm, is a fine to coarse powder consisting of microgametophytes (pollen grains), which carry the male gametes of seed plants. Pollen grain is surrounded by a cellulose cell wall and a thick, tough outer wall made of sporopollenin. Pollen is produced in the microsporangium (contained in the anther of an angiosperm flower or male cone of a coniferous plant). Pollen grains come in a wide variety of shapes, sizes, and surface markings characteristic of the species. Most, but certainly not all, are spherical. Pollen grains of pines, firs, and spruces are winged. The smallest pollen grain is around 6µm (0.006mm) in diameter. The study of pollen is called palynology and is highly useful in paleontology, archeology, and forensics.

Except in the case of some submerged aquatic plants the mature pollen-grain has a double wall, a thin delicate wall of unaltered cellulose and a tough outer cuticularized exospore or exine. The exine ofter bears spins or warts, or is variously sculptured, and the character of the markings is often of value for identifying genus, species, or even cultivar or individual.

Innumerable stories and even more rumors exist about the mysterious powers of pollen and its nutritional value. Pollen is frequently called the "only perfectly complete food". High performance athletes are quoted as eating pollen, suggesting their performance is due to this "miracle food", just as the "busy bee" represents a role model for an active and productive member of society.

Pollens from different plants will have different shapes and sizes because of the different requirements for the pollination of different flowers. In this project, different pollens will be examined with different techniques including SEM, light microscopy, x-ray analysis, etc.

Materials and methods

Three kinds of pollens are collected from tulip, jonquilla daffodils and hyacinth respectively. Techniques used: coating, secondary electron detector, x-ray analysis, colorization, light microscopy and electron flight simulation. The pollens are put onto the holder and then put into the simple DC sputtering system to coat the samples for more than 60sec. After the coating, the samples are put on the stage in the SEM chamber. Secondary electron detector is used first to examine the samples and accelerating voltage, working distance and magnification are changed. With the images obtained above, colorization is used and different colors are chose for different pollen images. Light microscopy is used to get the pictures for these pollens with their initial colors. Then the x-ray analysis are used with the working distance is fixed onto 20mm and the accelerating voltage is 10KV. Electron flight simulation is operated assuming the composition of pollen being C16H32O.

From these SEM images, we can see that the pollens from hyacinth are elliptic. It is sharp on both sides with the middle part swelling. There is a valley-like line on the pollen. The surface is not smooth and distributed with little concaves. The average size of this kind of pollen is about 50μm.

b. Light microscopy results

Figure 2. LM pictures of pollens from hyacinth.

From the light microscopy pictures, we can see that color of the pollens from the hyacinth is light yellow. The shape is as what we have got from the SEM detection. Also some small or smaller particles can be found in these pictures. This is maybe because that these pollens are immature.

c. X-ray analysis result

Figure 3. X-ray analysis of pollens from hyacinth.

The elements detected by the x-ray analysis are Au, C and O. Gold is from coating. From this result, we can see that the pollens are composed of organic compounds and no rare elements exist.

From these images, we can see that the shape of the pollens from tulip is like dumpling with the surface full of bumps. Some pollen grains are like cauliflower with a very short stem and a puffy head. The average size of this kind of pollen is 40μm.

b. Light microscopy results

Figure 5. LM pictures of pollens from tulip flower.

From the light microscopy pictures, we can see that the color of the pollen grains is purple with the same shape as detected by the SEM. There are different sizes pollen grains in the right picture. This is maybe because the smaller ones are not mature enough and grow to the full size.

c. X-ray analysis result

Figure 6. X-ray analysis of pollens from tulip flowers.

The result is the same as that for the pollen from hyacinth and it is composed with C and O. Gold is from coating.

The shape of the pollens from jonquilla daffodils is also elliptic while with the deep and honeycomb-like concaves which is different from that of hyacinth pollens. The pollens are like the rolled leaves with one side covered with the other side. The opened pollen is also detected. It seems that only one pole exists inside. The average size is about 50μm.

b. Light microscopy results

Figure 8. LM pictures of pollens from jonquilla daffodils flower.

From these pictures, we can see that the color of the pollen is also light yellow with the same size as detected by SEM.

c. X-ray analysis result

Carbon, oxygen and gold are still detected for the pollen from jonquilla daffodils and gold are from coating. Except this, small amount of phosphorus is also found.

Figure 9. X-ray analysis of pollens from jonquilla daffodils flower.

d. Electron flight simulation

The methyl esters of fatty acids from 35 commercial samples of bee-collected pollen were ever analyzed by gas-liquid chromatography using 15 percent diethylene glycolsuccinate (D.E.G.S.) as fixed phase and programmed temperature at 140°C to 200°C at 1.4°C /min. The detector and injector temperature were held at 250°C [1]. Of the 31 fatty acids have been isolated only 16 were identified: C8:0; C10:0; C12:0; C14:0; C16:0; C18:0; C18:1; C19:0; C21:0; C18:2; C22:0; C23:0; and C24:0. The principal fatty acid was palmitic C16:0 with 27.2 percent. So we assume that the main molecular formula for the pollens from tulip, hyacinth and jonquilla daffodils is also C16H32O and simulate the interaction between electron beam and the samples with the Electron Flight Simulator Demo software. The simulation result is showed as following.

Discussion

From the results above, we can see pollens from different flowers have different sizes and shapes. The pollens from hyacinth and jonquilla daffodils are longer than that from tulip with the surface covered with concaves. The surface of the pollen from the tulip is covered with bumps.

The transfer of pollen grains to the female reproductive structure is called pollination. This transfer can be mediated by the wind, in which case the plant is described as anemophilous (literally wind-loving). Anemophilous plants typically produce great quantities of very lightweight pollen grains, often with air-sacs, and generally have inconspicuous flowers. Entomophilous (literally insect-loving) plants produce pollen that is relatively heavy, sticky and protein-rich, for dispersal by insect pollinators attracted to their flowers.

From the x-ray analysis, the compositions of these pollens are almost the same with carbon and hydrogen as the prominent elements. It means that they have the analogous density. Also from the SEM image, their volumes are also similar. The pollens have the similar weight. From the SEM and light microscopy, we can see that the shapes are quite different. It is probably because of the different requirement for the pollination of the flowers. For tulip, the flower will not be opened totally through its blooming period. Pollinator like bees apparently the chief means of seed dispersal. The surface isn’t smooth so that it will be easy for the insects to carry. While for the pollens from the hyacinth and jonquilla daffodils, their flowers can open totally so that wind will pollinate so that there isn’t bump on the surface. Pollens from entomophilous plants do not become airborne, so they cannot get into your nose and cause allergies [2].

The color of the pollen from the tulip is red while those from hyacinth and jonquilla daffodils are both light yellow. The more the color of the pollens, the more it will evoke the nervous system of the eyes. From this point, we also can tell that the bright color of the pollens from tulip will make it easier to be recognized by the insects and carried away by them. The colors are decided by the constituents of the pollens. It means that although three kinds of pollens are all composed of carbon and oxygen but they form different fatty acid which can bring different colors for pollens.

Conclusions

The average sizes of pollens from hyacinth and jonquilla daffodils are both 50µm, while the tulip 40µm. Pollens have different sizes and shapes because of the different pollination requirements of the flowers. The mainly compositions of these pollens are carbon and oxygen with only tulip having small amount of phosphorus. These carbon and oxygen form different fatty acids and provide different colors for the pollens.

Acknowledgement

Thanks Brian for his lectures and help with the project. Also thanks those Anemophilous flowers for giving the allergic reaction on me.